Vertical Bloch Line (VBL) Memory is a recently conceived, integrated, solid-state, block-access, VLSI memory which offers the potential of 1 Gbit/cm.sup.2 areal storage density, gigabit per second data rates, and submillisecond average access times simultaneously at relatively low mass, volume, and power values when compared to alternative technologies. VBLs are micromagnetic structures within magnetic domain walls which can be manipulated using magnetic fields from integrated conductors. The presence or absence of VBL pairs are used to store binary information. At present, efforts are being directed at developing a single-chip memory using 25 Mbit/cm.sup.2 technology in magnetic garnet material which integrates, at a single operating point, the writing, storage, reading and amplification functions needed in a memory. The densities are a function of stripe width and line feature width, which are defined respectively by the magnetic garnet material and the lithographic process.
In a VBL memory, information is stored using VBL pairs in magnetic stripe domains in magnetic garnets. The presence or absence of a vertical Bloch line pair in a bit-cell location defines a binary "1" and "0", respectively. Input to the chip is performed by converting currents into magnetic bubbles and then into VBL pairs. Output sensing is performed by converting VBL pairs into magnetic bubbles and sensing magnetic bubbles magnetoresistively.
One prior art design uses the magnet garnet, (BiYGdHoCa).sub.3 (FeGeSi).sub.5 O.sub.12, as the storage medium. The thickness, stripe width, collapse field, saturation magnetization, and anisotropy field of the film is approximately 2.4 .mu.m, 2.4 .mu.m, 230 Oe, 450 Oe, and 1800 Oe, respectively. The film is grown epitaxially on a non-magnetic gadolinium-gallium-garnet (GGG) substrate. These films are transparent but also have a large Faraday rotation, so that magnetic stripes, magnetic bubbles, and, under certain conditions, VBLs can be observed magneto-optically with polarized light using the Faraday effect in a polarized light microscope.
The magnetic garnet has perpendicular magnetic anisotropy so that magnetization lies perpendicular to the film plane, with the bulk of the film magnetized in one direction, and the stripes in the opposite direction. A magnetic domain wall is the boundary between the stripe magnetization and the magnetization of the rest of the film. A twist of magnetization in the domain wall in the plane of the film is a VBL, and two such twists form a VBL pair. If the chirality, or sense of rotation, of the VBLs in the wall is the same, the VBL pair is stable, with a size calculated to be much less than 1 .mu.m. The VBL pair is bound together energetically by VBL demagnetizing field energy and magnetic exchange energy.
A number of articles on VBL memory have been published are listed herein by way of background reference:
1. "Vertical Bloch Line Memory" by R. R. Katti, J. C. Wu and H. L. Stadler; 1990 NASA Space Engineering Research Center--Symposium on VLSI Design, pgs. 8.3.1 to 8.3.20.
2. "Integrated Vertical Bloch Line Memory" by R. R. Katti, J. C. Wu and H. L. Stadler; 1990 NASA Technology 2000 Conference Proceedings, pgs. 25-33.
3. "Design and Characteristics for Vertical Bloch Line Memory Using Ring-Shaped Domain" by H. Matsutera, K. Mizuno and Y. Hidaka; IEEE Transactions on Magnetics, Vol. Mag-23, No. 5, September 1987, pgs. 2320-2325.
4. "Operation of a VBL Memory Write Gate" by J. C. Wu and F. B. Humphrey; IEEE Transactions on Magnetics, Vol. Mag-21, No. 5, September 1985, pgs. 1773-1775.
5. "Chip Organization of Bloch Line Memory" by T. Suzuki, H. Asada, K. Matsuyama, E. Fujita, Y. Saegusa, K. Morikawa, K. Fujimoto, M. Shigenobu, K. Nakashi, H. Takamatsu, Y. Hidaka, and S. Konishi; IEEE Transactions on Magnetics, Vol. Mag-22, No. 5, September 1986, pgs. 784-789.
6. "Vertical Bloch Line Memory" by F. B. Humphrey and J. C. Wu; IEEE Transactions on Magnetics, Vol. Mag-21, No. 5, September 1985, pgs. 1762-1766.